The present invention relates to a system for cooling liquid fuel components subject to conduction and radiation heating, and in particular, to a system for directing pressurized ambient temperature air to an annulus located between a component and a sleeve installed around the component or cool liquid to a tube in physical contact with the component.
Gas turbines typically operate on natural gas fuel, with fuel oil (typically No. 2 distillate) often used as a contingency for periods of gas unavailability. When a gas turbine is operating on natural gas fuel, the fuel oil typically remains in liquid fuel lines (e.g., piping/tubing) leading to the combustor nozzles of the gas turbine. The stagnant fuel oil in the liquid fuel lines is often exposed to the turbine compartment air temperatures of up to 250° F., and turbine surfaces of up to 800° F.
Typically, a gas turbine has a number of combustors positioned around the turbine, each combustor having a gas fuel nozzle and a liquid fuel nozzle. When the turbine is running on one type of fuel, the nozzle for the other type of fuel must be purged of the other type of fuel. Thus, for example, when a turbine is switched from running on fuel oil back to running on natural gas fuel, the fuel oil in the liquid fuel nozzle must be purged. Over time, this fuel nozzle “purge air” fills some portion of the liquid fuel piping leading up to the liquid fuel nozzle as the level of fuel oil in the piping recedes due to leakage past upstream shutoff valves, and by thermal expansion and contraction with no make-up supply of liquid fuel. This air-oil interface on the coated surfaces of the piping system and valves (e.g., check valves, ball valves, spool valves, etc.) in the presence of the radiated, conducted, and convected heat, leads to coke formation in the liquid fuel piping, resulting in flow restriction and inoperable valves. Eliminating any one of the three ingredients required for coke formation (i.e., fuel oil, heat and air) will prevent coking. Since it is not practical to eliminate fuel oil or air in a turbine, it would be beneficial to eliminate the heating of the liquid fuel lines, thereby resulting in the prevention of coking in the liquid fuel line piping and valves.
Prior attempts have been made to direct turbine compartment cooling air flow to areas subject to coking, but sufficient temperature cooling could not be attained. Typically, a combustor in a turbine operates at a temperature well over 2000° F. The heat from the combustors radiates toward components, such as the fuel oil piping and valves, sitting in the turbine enclosure. Even with attempts to ventilate the enclosure that included directing cooling air toward components subject to coking, air temperatures of 300° F. around such components was still typical. Lower temperatures could not be attained, even though 30,000 cubic feet per minute of air is typically moving through the enclosure of a turbine.